The purpose of this project is to identify quantitatively the postural control characteristics of the normal and vestibular deficient human in an upright attitude. The second phase of the research project will examine the vestibulo-spinal and converging visual and proprioceptive mechanisms. The ultimate goal is to characterize the transfer characteristics between head motions detected by the vestibular system and control of the subject's center-of-mass force trajectories. Performance of normal subjects under stable and under unstable contitions will provide additional information about the characteristics of the vestibulo-spinal and converging control systems. The final goal of the project series will be to develop a rapid screening method for evaluation of patients complaining of spatial disorientation.